#define _CRT_SECURE_NO_WARNINGS
typedef struct ListNode ListNode;
struct ListNode* FindKthToTail(struct ListNode* pListHead, int k) {
    if (pListHead == NULL) {
        return NULL;
    }
    ListNode* fast, * slow;
    slow = fast = pListHead;
    while (k) {
        if (fast) {
            fast = fast->next;
        }
        else {
            return NULL;
        }
        k--;
    }
    while (fast) {
        slow = slow->next;
        fast = fast->next;
    }
    return slow;
}